1 2D8-7/45-II air compressor introduction
The overall structure of the 2D8-7/45-II air compressor is two columns of symmetric balance type (I, II is a column, II, IV is a column), four stages of compression, each stage has a separate cooler and water separation Device. The cylinder and packing parts are oil-free. The compressor is directly driven by the coupling and the motor.
2 choice of exhaust volume measurement method
There are many methods for measuring the displacement of a compressor, such as a flow meter method, a filling method, a weighing method, and a heat balance method.
Among them, the heat balance method is more suitable for on-site tracking measurement of compressor users. However, the measurement of the inlet and outlet temperature and the amount of condensed water of the interstage cooler cooling water and compressed air are required to be very accurate. Otherwise, the measured displacement error is large.
Although the filling method is simple and easy, the 2D8-7/45-II air compressor is not equipped with a gas storage tank on site, and it is obviously uneconomical to process a gas storage tank only for temporary verification measurement.
There are many types of flowmeter methods, among which differential pressure flowmeters are the most widely used. The differential pressure type flowmeter generally consists of a throttling device, a differential pressure gauge, and a differential pressure signal line connecting the two; and the throttling device usually has two types of nozzle throttling and orifice throttling. Satisfactory measurements can be obtained whether nozzles or orifice plates are used for throttling. Compressor displacement measurement specifications in many countries around the world allow for the use of nozzle or orifice throttling to measure displacement. Nozzle throttling measures the displacement of the compressor, which has been widely used in China's compressor industry. The national standard GB3853-83 gives detailed specifications for its measurement method. The measuring device adopts an open system, and the gas is firstly regulated by a large-volume container, and then flows through a pressure regulating valve to a low-pressure tank under a reduced pressure state, and finally discharged to the atmosphere through a nozzle. Because it is an open system and the device is more complicated, it is generally used only when the compressor manufacturer performs the test and identification of its products.
The orifice throttling measuring device can measure the displacement in the closed system, and the device is simpler than the nozzle throttling, so it is more suitable for the measurement of the on-site displacement of the compressor for industrial process.
In summary, it was decided to use the orifice plate throttling device to measure the on-site displacement of the 2D8-7/45-II air compressor.
On-site installation and flow measurement of 3 throttling devices
Design and manufacture various parts of the throttling device (front ring chamber, rear chamber, orifice plate, flange, etc.), install the throttle device and differential pressure signal pipeline on the compressor IV exhaust line, CGS-50 Double tube differential pressure gauge, its maximum working pressure is 5MPa (50kgf/cm2), differential pressure measurement range is 0~09) 105 Pa (0~700mmHg); 3 is J21H-64C stop valve, nominal pressure is 64 MPa, use temperature +200 %; 2 is the differential pressure signal tube, 10) 1 of the copper tube. After the installation is completed and tested, the displacement of the exhaust gas is measured before and after the compressor transformation, and good results are obtained.
1 throttling device 2 differential pressure signal tube (10) 1) 3 shut-off valve 4CGS-50 double-tube differential pressure gauge 5 exhaust pipe (89) 4)
Figure 3: Differential pressure signal pipeline installation diagram Through the practice of measuring the displacement of the compressor in this compressor, we realized that the on-site measurement of the displacement of the piston compressor with the standard orifice plate throttling device should pay attention to the following points. (1) When the parts of the throttling device are processed by the measuring unit, it must be strictly in accordance with the requirements and requirements of the relevant standards to ensure the processing accuracy, otherwise it will cause a large flow measurement error.
(2) Differential pressure in the design of the throttling device! The larger p is, the smaller the orifice orifice diameter is, and the smaller the diameter ratio is, the shorter the straight pipe section upstream of the throttling device is. Therefore, the differential pressure should be determined by considering the layout of the exhaust line on site and the measurement range of the selected differential pressure gauge! p value. That is to make it! p is in the optimum range of the differential pressure gauge measurement range, and the straight pipe section required upstream of the throttling device is as short as possible (because it is difficult to find the required length on the compressor pipeline due to space limitations at the site) Pipe section).
(3) Take necessary measures to reduce or eliminate the pressure pulsation in the compressor line as much as possible.
(4) In order to ensure the roundness, roughness and other requirements of the pipe in the straight pipe upstream of the throttling device, the straight pipe segment can be replaced with a new pipe if conditions permit, to reduce the measurement error.
4 Conclusion
Standard orifice throttling devices are used in a wide range of applications in industrial measurement and control. The device has the advantages of simple structure, convenient installation, low cost and accurate measurement data, and is therefore particularly suitable for measuring the on-site displacement of compressors for industrial processes.
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